Addition of soil protists may enhance performance of agrochemical seed treatments

Abstract

Chemicals are an integral part of modern agriculture and are applied through a variety of methods. Some agrochemicals used for crop protection are absorbed by the roots prior to translocation to the rest of the plant. To be absorbed by the root, the agrochemical must first be transported through the soil, often by water. Some agrochemicals suffer from poor water-based soil transmission due to their chemical properties, limiting their application as a traditional seed treatment. Two agrochemicals with poor water-based soil transmission are Chlorantraniliprole and Spinosad. Soil protists are an important component of the soil microbial community. Certain soil protists have been shown to facilitate the transport and target delivery of suspended particles and bacteria through soil and soil-like structures. Here, we provide practical evidence that a soil protist, Colpoda sp., when co-inoculated with an agrochemical seed treatment, can substantially and robustly reduce subsequent pest feeding damage versus application of the agrochemical alone. Using maize (Zea mays L.) and fall armyworm, Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae), in a plant damage assay, we compare pest feeding damage and pest mortality for leaf samples from plants whose seeds were treated with only protists, only agrochemical, or agrochemical + protists. We discover, for both agrochemicals tested, that co-inoculation of protists with agrochemical increases protection in leaves versus agrochemical alone. Protist amendment is a simple, natural, chemical-free, soil-based transport enhancer that may be widely useful in a variety of contexts including more sustainable agriculture methods and cost-effective integrated pest management.